In a copending application of Samuel E. Pence Jr., Ser. No. 241,816, filed Apr. 6, 1972, now Pat. No. 3,765,488 for Well Treating Method, there is disclosed a method for treating a subterranean formation by injecting thereinto an essentially anhydrous mixture comprising liquid carbon dioxide and an alcohol, such as methanol, gelled to a viscosity of at least 10 centipoises with a hydroxyalkyl cellulose such as hydroxypropylcellulose. Said method achieved rapid commercial success since it made possible the use of propping agents such as sand with the volatile fracturing fluids, such as liquid carbon dioxide as taught in U.S. Pat. No. 3,108,636 or mixtures of liquid carbon dioxide with liquefied petroleum gas (LPG) as disclosed in U.S. Pat. No. 3,368,627, whereby natural gas production can be stimulated by fracturing techniques without leaving undesired residues in the producing formation.
In field practice, however, the available alcohol-soluble hydroxypropylcellulose materials have shown certain disadvantages. For example, these materials are characterized by a degree of plasticity such that caking can occur in storage or shipment and the caked material becomes difficult to disperse and dissolve in alcohol with the equipment available for a well-head operation. Further it has been found that even when relatively finely divided hydroxypropylcellulose is well dispersed in an alcohol, such as methanol, the resulting dispersion requires a considerable period of aging to accomplish complete solvation of the hydroxypropylcellulose and to develop the desired viscosity of the gelled alcohol. Thus, in practice, it has generally been necessary to disperse the hydroxypropylcellulose in the large amount of methanol necessary for a fracturing job on one day and allow the aging to proceed overnight before the gelled alcohol is ready for use. Finally it has been found that available supplies of hydroxypropylcellulose are soluble only to the extent of about 100 pounds per 1000 gallons of anhydrous methanol at ambient temperatures which places an upper limit on attainable viscosities with such agents.
Accordingly, it is an object of the present invention to provide compositions containing liquid carbon dioxide and a gelled substantially anhydrous alcohol comprising an improved gelling agent and to provide a method for treating subterranean formations with the improved composition.